1. Field of the Invention
The present invention relates to an optical transmission/reception module for coupling a light-emitting element and a light-receiving element with respect to an optical fiber for passing therethrough transmission light and reception light of a plurality of different wavelengths.
2. Description of the Related Art
FIG. 6 is a cross sectional view of a conventional optical transmission/reception module. As shown in FIG. 6, the housing of the optical transmission/reception module roughly comprises four blocks. They are a center block 1, a LD (laser diode) block 2, a PD (photodiode) block 3, and a fiber block 4. A partial wave filter 5 is mounted in the center block 1. A laser diode 6 (D6), being a light-emitting element, and a lens holder 8, supporting a lens 7, are mounted to the LD block 2. A photodetector 9 (PD9), being a light-receiving element, and a lens holder 11, supporting a lens 10, are mounted to the PD block 3. An optical fiber 12 and a lens holder 14, supporting a lens 13, are mounted to the fiber block 4.
A transmission light of wavelength .lambda.1 from the LD 6, which has been transformed into parallel light beams by a lens 7 at the LD block side, passes through the partial wave filter 5 at the center block 1. Then, the parallel transmission light beams are gathered by the lens 13 in the fiber block 4, and passes through the optical fiber 12 from an end surface thereof in order to be transmitted. On the other hand, a reception light of wavelength .lambda.2, which has been scattered at an end surface of the optical fiber 12, is transformed into parallel light beams by the lens 13 at the fiber block 4. Then, the parallel reception light beams are reflected by the partial wave filter 5 in the center block 1, and gathered by the lens 10 at the PD block 3 in order to be received by the PD 9.
In assembling an optical transmission/reception module having such a structure, the LD block 2 and the fiber block 4 are affixed to the center block 1 by laser welding or the like, with their optical axes aligned, whereby optical axes alignments for the transmission light are performed. Thereafter, the center block 1 and the PD block 3 are affixed together by laser welding or the like, with their optical axes aligned, whereby optical axes alignments for the reception light are performed.
In the above-described conventional optical transmission/reception module, however, the partial wave filter 5 is disposed obliquely at a predetermined mounting angle of, for example, 45 degrees in the center of a space in the center block 1. Therefore, even in cases where the partial wave filter 5 is mounted to the center block 1 either directly or through a transparent supporting member, it is difficult to form a mounting reference surface for the partial wave filter 5 in the center block 1 with high precision, causing the partial filter 5 to be mounted less precisely at the desired mounting angle.
In addition, the optical axes alignments for four blocks 1 to 4 must be made, so that optical axes alignments cannot be made with high precision. Further, the four blocks 1 to 4, which are small in size, must be integrally welded together or the like, resulting in higher assembly costs.